These constants are available starting with PHP 7.0.0. Please note that
some of them may not be available on your system.

Note:

You may wish to read the below notes in conjunction with the manpage for
setrlimit() on your specific operating system, as there
is variance in how these limits are interpreted, even across operating
systems that claim to implement POSIX in full.

The maximum amount of CPU time that the process can use, in seconds.
When the soft limit is hit, a SIGXCPU signal will be
sent, which can be caught with pcntl_signal().
Depending on the operating system, additional SIGXCPU
signals may be sent each second until the hard limit is hit, at which
point an uncatchable SIGKILL signal is sent.
See also set_time_limit().

The maximum number of bytes that can be allocated for POSIX message
queues. PHP does not ship with support for POSIX message queues, so this
limit will not have any effect unless you are using an extension that
implements that support.